remove xfermode from public api

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4020

CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I19cd056f2af778f10e8c6c2b7b2735593b43dbac
Reviewed-on: https://skia-review.googlesource.com/4020
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gm/color4f.cpp b/gm/color4f.cpp
index c1535cc..b5cda9f 100644
--- a/gm/color4f.cpp
+++ b/gm/color4f.cpp
@@ -47,7 +47,7 @@
 }
 
 static sk_sp<SkColorFilter> make_cf2() {
-    return SkColorFilter::MakeModeFilter(0x8044CC88, SkXfermode::kSrcATop_Mode);
+    return SkColorFilter::MakeModeFilter(0x8044CC88, SkBlendMode::kSrcATop);
 }
 
 static void draw_into_canvas(SkCanvas* canvas) {